diff --git a/components/driver/include/driver/spi_master.h b/components/driver/include/driver/spi_master.h
index ca8246889..04f2ba1f2 100644
--- a/components/driver/include/driver/spi_master.h
+++ b/components/driver/include/driver/spi_master.h
@@ -150,6 +150,10 @@ typedef struct spi_device_t* spi_device_handle_t;  ///< Handle for a device on a
  * @warning If a DMA channel is selected, any transmit and receive buffer used should be allocated in
  *          DMA-capable memory.
  *
+ * @warning The ISR of SPI is always executed on the core which calls this
+ *          function. Never starve the ISR on this core or the SPI transactions will not
+ *          be handled.
+ *
  * @return
  *         - ESP_ERR_INVALID_ARG   if configuration is invalid
  *         - ESP_ERR_INVALID_STATE if host already is in use
diff --git a/components/driver/include/driver/spi_slave.h b/components/driver/include/driver/spi_slave.h
index 9ad4b9126..ba0ce1de6 100644
--- a/components/driver/include/driver/spi_slave.h
+++ b/components/driver/include/driver/spi_slave.h
@@ -71,10 +71,14 @@ struct spi_slave_transaction_t {
  *                 it. The SPI hardware has two DMA channels to share. This parameter indicates which
  *                 one to use.
  *
- * @warning If a DMA channel is selected, any transmit and receive buffer used should be allocated in 
+ * @warning If a DMA channel is selected, any transmit and receive buffer used should be allocated in
  *          DMA-capable memory.
  *
- * @return 
+ * @warning The ISR of SPI is always executed on the core which calls this
+ *          function. Never starve the ISR on this core or the SPI transactions will not
+ *          be handled.
+ *
+ * @return
  *         - ESP_ERR_INVALID_ARG   if configuration is invalid
  *         - ESP_ERR_INVALID_STATE if host already is in use
  *         - ESP_ERR_NO_MEM        if out of memory
@@ -86,7 +90,7 @@ esp_err_t spi_slave_initialize(spi_host_device_t host, const spi_bus_config_t *b
  * @brief Free a SPI bus claimed as a SPI slave interface
  *
  * @param host SPI peripheral to free
- * @return 
+ * @return
  *         - ESP_ERR_INVALID_ARG   if parameter is invalid
  *         - ESP_ERR_INVALID_STATE if not all devices on the bus are freed
  *         - ESP_OK                on success
@@ -110,7 +114,7 @@ esp_err_t spi_slave_free(spi_host_device_t host);
  *                   into the transaction description.
  * @param ticks_to_wait Ticks to wait until there's room in the queue; use portMAX_DELAY to
  *                      never time out.
- * @return 
+ * @return
  *         - ESP_ERR_INVALID_ARG   if parameter is invalid
  *         - ESP_OK                on success
  */
@@ -120,19 +124,19 @@ esp_err_t spi_slave_queue_trans(spi_host_device_t host, const spi_slave_transact
 /**
  * @brief Get the result of a SPI transaction queued earlier
  *
- * This routine will wait until a transaction to the given device (queued earlier with 
+ * This routine will wait until a transaction to the given device (queued earlier with
  * spi_slave_queue_trans) has succesfully completed. It will then return the description of the
- * completed transaction so software can inspect the result and e.g. free the memory or 
+ * completed transaction so software can inspect the result and e.g. free the memory or
  * re-use the buffers.
  *
  * It is mandatory to eventually use this function for any transaction queued by ``spi_slave_queue_trans``.
  *
  * @param host SPI peripheral to that is acting as a slave
- * @param[out] trans_desc Pointer to variable able to contain a pointer to the description of the 
+ * @param[out] trans_desc Pointer to variable able to contain a pointer to the description of the
  *                   transaction that is executed
  * @param ticks_to_wait Ticks to wait until there's a returned item; use portMAX_DELAY to never time
  *                      out.
- * @return 
+ * @return
  *         - ESP_ERR_INVALID_ARG   if parameter is invalid
  *         - ESP_OK                on success
  */
@@ -143,16 +147,16 @@ esp_err_t spi_slave_get_trans_result(spi_host_device_t host, spi_slave_transacti
  * @brief Do a SPI transaction
  *
  * Essentially does the same as spi_slave_queue_trans followed by spi_slave_get_trans_result. Do
- * not use this when there is still a transaction queued that hasn't been finalized 
+ * not use this when there is still a transaction queued that hasn't been finalized
  * using spi_slave_get_trans_result.
  *
  * @param host SPI peripheral to that is acting as a slave
- * @param trans_desc Pointer to variable able to contain a pointer to the description of the 
+ * @param trans_desc Pointer to variable able to contain a pointer to the description of the
  *                   transaction that is executed. Not const because we may want to write status back
  *                   into the transaction description.
  * @param ticks_to_wait Ticks to wait until there's a returned item; use portMAX_DELAY to never time
  *                      out.
- * @return 
+ * @return
  *         - ESP_ERR_INVALID_ARG   if parameter is invalid
  *         - ESP_OK                on success
  */
diff --git a/components/driver/spi_master.c b/components/driver/spi_master.c
index a29182592..7d8932f5e 100644
--- a/components/driver/spi_master.c
+++ b/components/driver/spi_master.c
@@ -442,14 +442,14 @@ esp_err_t spi_bus_add_device(spi_host_device_t host, const spi_device_interface_
     duty_cycle = (dev_config->duty_cycle_pos==0) ? 128 : dev_config->duty_cycle_pos;
     eff_clk = spi_cal_clock(apbclk, dev_config->clock_speed_hz, duty_cycle, (uint32_t*)&clk_reg);
     int freq_limit = spi_get_freq_limit(!(spihost[host]->flags&SPICOMMON_BUSFLAG_NATIVE_PINS), dev_config->input_delay_ns);
-    //GPIO matrix can only change data at 80Mhz rate, which only allows 40MHz SPI clock.
-    SPI_CHECK(eff_clk <= 40*1000*1000 || spihost[host]->flags&SPICOMMON_BUSFLAG_NATIVE_PINS, "80MHz only supported on iomux pins", ESP_ERR_INVALID_ARG);
+
     //Speed >=40MHz over GPIO matrix needs a dummy cycle, but these don't work for full-duplex connections.
     spi_get_timing(!(spihost[host]->flags&SPICOMMON_BUSFLAG_NATIVE_PINS), dev_config->input_delay_ns, eff_clk, &dummy_required, &miso_delay);
     SPI_CHECK( dev_config->flags & SPI_DEVICE_HALFDUPLEX || dummy_required == 0 ||
             dev_config->flags & SPI_DEVICE_NO_DUMMY,
-"When GPIO matrix is used in full-duplex mode at frequency > %.1fMHz, device cannot read correct data.\n\
-Please note the SPI can only work at divisors of 80MHz, and the driver always tries to find the closest frequency to your configuration.\n\
+"When work in full-duplex mode at frequency > %.1fMHz, device cannot read correct data.\n\
+Try to use IOMUX pins to increase the frequency limit, or use the half duplex mode.\n\
+Please note the SPI master can only work at divisors of 80MHz, and the driver always tries to find the closest frequency to your configuration.\n\
 Specify ``SPI_DEVICE_NO_DUMMY`` to ignore this checking. Then you can output data at higher speed, or read data at your own risk.",
             ESP_ERR_INVALID_ARG, freq_limit/1000./1000 );